The present invention relates generally to high speed connectors, and more particularly to high speed backplane connectors, with reduced crosstalk and improved performance.
High speed connectors are used in many data transmission applications particularly in the telecommunications industry. Signal integrity is an important concern in the area of high speed and data transmission for components need to reliably transmit data signals. The high speed data transmission market has also been driving toward reduced size components.
High speed data transmission is utilized in telecommunications to transmit data received from a data storage reservoir or a component transmitter and such transmission most commonly occurs in routers and servers. As the trend of the industry drives toward reduced size, the signal terminals in high speed connectors must be reduced in size and to accomplish any significant reduction in size, the terminals of the connectors must be spaced closer together. As signal terminal are positioned closer together, signal interference occurs between closely spaced signal terminals especially between pairs of adjacent differential signal terminals. This is referred to in the art as “crosstalk” and it occurs when the electrical fields of signal terminals abut each other and intermix. At high speeds the signal of one differential signal pair may drift and cross over to an adjacent or nearby differential signal pair. This affects signal integrity of the entire signal transmission system. The reduction of crosstalk in high speed data systems is a key goal in the design of high speed connectors.
Previously, reduction of crosstalk was accomplished primarily by the use of shields positioned between adjacent sets of differential signal terminals. These shields were relatively large metal plates that act as an electrical reference point, or barrier, between rows or columns of differential signal terminals. These shields add significant cost to the connector and also increase the size of the connector. The shields may act as large capacitive plates to increase the coupling of the connector and thereby lower the impedance of the connector system. If the impedance is lowered because of the shields, care must be taken to ensure that it does not exceed or fall below a desired value at that location in the connector system. The use of shields to reduce crosstalk in a connector system requires the system designer to take into account their effect on impedance and their effect on the size of the connector.
Some have tried to eliminate the use of shields and rely upon individual ground terminals that are identical in shape and dimension to that of the differential signal terminals with which they are associated. However, the use of ground terminals the same size as the signal terminals leads to problems in coupling which may drive up the system impedance. The use of ground terminals similarly sized to that of the signal terminals requires careful consideration to spacing of all the terminals of the connector system throughout the length of the terminals. In the mating interface of high speed connector, impedance and crosstalk may be controlled due to the large amounts of metal that both sets of contacts present. It becomes difficult to match the impedance within the body of the connector and along the body portions of the terminals in that the terminal body portions have different configurations and spacing than do the contact portions of the terminals. This difficulty increases in areas of the connector where the terminals are mounted to their insulative support frames or housings. Adding more connector housing support material, such as plastic, may reduce the amount of air to be used as a dielectric, which may promote an impedance discontinuity so that due consideration must be made with respect to the manner in which the terminals are mounted in the connector.
The present invention is therefore directed to a high speed connector that overcomes the above-mentioned disadvantages and which uses ground terminals in the form of a plurality individual shields, which are associated with each differential signal terminal pair to control crosstalk, and in which the connector housing, or frame, has a structure that assists in controlling the impedance of the terminals in their extent through the connector frame.